High volume printing of books, brochures, and other multi-page documents typically involves imposition. Imposition is the process of laying out the pages of a document such that they are in numerical order after a larger printed sheet, known as a signature, has been folded into multiples of four pages that make up a section of the document. Before printing the signatures with high-volume, double-sided printers, it is common practice to print a set of proofs using an imposition proofing printer.
Imposition proofing printers are typically relatively large, single-sided, tractor-fed, ink-jet printers. These printers first print one side of a signature on a large sheet of tractor-fed paper. An operator then turns the paper over and threads it back onto the printer's tractor feed mechanism so that the printer can print the other side.